(1) Field of the Invention
The present invention relates to a motor driven type flow control valve to be used for controlling the flow rate of a fluid and, more particularly, to a flow control valve to be applied to an exhaust gas recirculation valve for recirculating the exhaust gas of an internal combustion engine into the intake system
(2) Description of the Related Art
An exhaust gas recirculation valve for recirculating exhaust gas of an internal combustion engine into the intake system is exemplified by a system for controlling the exhaust gas flow through a passage in a valve housing by actuating a lift type valve member by a step motor. Such a system is described in Japanese Laid-Open Patent No. 76748/1986.
Such a recirculation valve is constructed by fixing the front portion of the step motor on the end portion of the valve housing, by a) projecting the valve step connected to the valve member in the valve housing into the motor housing, b) providing the step motor with an output shaft which can be moved only in an axial direction into the rotor through threaded portions, and c) connecting a coil spring for urging the valve member in a closing direction to the leading end of the valve stem. Thus, the recirculation valve is opened by pushing the leading end of the valve stem against the urging force of the coil spring with the output shaft of the motor.
However, a recirculation valve of this kind is deficient in that the output shaft of the step motor is liable to rock due to vibrations during running of the motor. The rocking is partly due to the output shaft being supported in the rotor only by the threaded portions, and partly because the leading end of the output shaft is apart from the valve stem when the valve is closed.
The coil spring used has a strong spring force to impart a predetermined sealing force to the valve member when this member is closed, such that the motor is required to move the valve member in a valve opening direction against the urging force of the coil spring. As a result, such a recirculation valve in the related art uses a relatively large-sized motor having a high torque such that it suffers due to increased power consumption.